how long does it take for benadryl to work

Benadryl (diphenhydramine) generally takes about 15 to 30 minutes to start working after being taken orally. It reaches its peak or maximum effect in about 1 to 3 hours. The effects of Benadryl usually last for about 4 to 6 hours. When applied topically, it takes longer, roughly around 24 hours to work. Injectable forms work faster than oral ones, kicking in almost immediately. The medication stays in the body for up to about 60 hours, but the noticeable effects wear off much earlier.